1. Field of the Invention
The present invention relates to a data multiplexer, a data multiplexing method, a data recording medium, a data recorder, a data demultiplexer and a data demultiplexing method which are adapted for use in recording, for example, digital video data with character data on a disk and reproducing such data therefrom.
2. Description of the Related Art
A television image on a screen is composed of a plurality of horizontal scanning lines. In the case of the NTSC system for example, one frame of image is composed of 525 horizontal scanning lines. Since an interlaced scanning process is adopted in the NTSC system, one frame is composed of an odd-field image and an even-field image.
Horizontal scanning lines are sequentially scanned from the uppermost left toward the lowermost right and, upon arrival of the horizontal scanning at the right end of the screen, it needs to be returned to the left end of the screen. And when the horizontal scanning has reached the lowermost end of the screen, it needs to be returned to the uppermost end. Therefore, a blanking interval is generated for returning the horizontal scanning in both horizontal and vertical directions. Consequently, on each of odd-field and even-field images as shown in FIG. 9, an area (effective area) usable substantially for display of a picture is rendered narrower than the area actually scanned.
For this reason, when video signals are digitized and recorded on a recording medium, merely the data of the effective area is encoded so as to reduce the amount to be encoded. For example, in an odd field as shown in FIG. 9A, a total of 240 horizontal scanning lines from the 21st to 260th are used as effective lines, while in an even field as shown in FIG. 9B, a total of 240 horizontal scanning lines from the 284th to 523rd are used as effective lines, and only the video signals of such effective lines are encoded.
FIG. 10 illustrates effective lines as an area in signals which change with a lapse of time. As shown in the diagram, an FID signal representing odd and even fields is inverted at each generation of a vertical synchronizing signal (VSYNC). And in an odd field, 240 lines (H) from the 21st to 260th lines (H) are used as effective ones, while in an even field, 240 lines (H) from the 284th to 523rd lines (H) are used as effective ones.
In transmitting such video signals, there is executed a process of superimposing character data or the like on a predetermined horizontal scanning line in a blanking area in a manner not to affect the essential picture of the effective area of the video signals. Regarding this technique, there are known CAPTAIN (Character and Pattern Telephone Access Information Network) system in Japan, teletext system in Europe, and closed caption system and EDS (Extended Data Services) in the United States.
The character data include characters such as alphabetic letters and numerals, and also a mosaic bit map used in the CAPTAIN system for example. Hereinafter such data will be termed pattern data.
For example, it is so prescribed that pattern data (caption data) is to be recorded on 21st H in the closed caption system, or on 21st H in an odd field and on 284th H in an even field in the EDS, respectively.
When data in the EDS for example is recorded by a helical-scanning video tape recorder, the recording state thereof is such as shown in FIG. 11. In this case, as illustrated, both 21st and 284th H, on which the pattern data is recorded, are recorded on the tape.
Therefore, in an operation of reproducing the video signal recorded on such a video tape and recording the reproduced signal on a disk after encoding the signal in accordance with a video CD standard based on the MPEG (Moving Pictures Expert Group)-1, the pattern data also is digitally recordable on the disk as well as the essential video data since, in the video CD standard, the effective lines for recording the pattern data are from 21st H to 260th H in an odd field and from 284th H to 523rd H in an even field.
In the video CD standard which is an application of the MPEG-1, effective lines are so prescribed as to include pattern-data insertion lines in both the closed caption and the EDS, whereby the pattern data is recordable on a disk. However, there exists a problem that, if the pattern data is inserted in any blanking interval anterior to the 21st H or in any blanking interval anterior to the 284th H, the pattern data is rendered unrecordable on the disk.
The present applicant proposed a contrivance in, e.g., Japanese Patent Application No. Hei 6-54706 relative to a technique of recording a video signal digitally on a disk in accordance with the MPEG-2 standard. In this prior proposal, unrequired data (pattern data) other than the essential video data is not recorded so as to achieve a superior picture quality in recording and reproducing the video data. More specifically, the 21st and 284th H are not recorded, and effective lines in an odd field are 240 H ranging from the 22nd to 261st H, while those in an even field are 240 H ranging from the 285th to 524th H.
Thus, in order to attain a superior picture quality, it is necessary to prepare a separate means to record pattern data.
The present invention has been accomplished in view of the circumstances mentioned above. It is therefore an object of the invention to realize proper recording and reproduction of even pattern data inserted on horizontal scanning lines at any positions. And another object of the invention resides in enabling exact recording and reproduction of pattern data without deteriorating the picture quality in comparison with the means employed in the video CD standard which is based on the MPEG-1.
According to a first aspect of the present invention, there is provided a data multiplexer for multiplexing at least digital moving picture data and pattern data. The data multiplexer comprises a packetizing means for forming the digital moving picture data and the pattern data into packets of a predetermined format, each packet consisting of a header and an actual data region; an adding means for adding, to the header of each packet, a flag to identify the moving picture data and the pattern data; and a multiplexing means for multiplexing the packets.
The pattern data is disposed in a vertical blanking period. In the NTSC system, the pattern data in each odd field may be character data disposed on the 21st horizontal scanning line, and the digital moving picture data in each odd field may be composed of a predetermined number of horizontal scanning lines after the 22nd line.
Also in the NTSC system, the pattern data in each even field may be character data disposed on the 284th horizontal scanning line, and the digital moving picture data in each even field may be composed of a predetermined number of horizontal scanning lines after the 285th line.
A packet of the pattern data and a packet of the digital moving picture data include, respectively, a time stamp indicative of decode or display timing.
A packet of the pattern data is prescribed by Private_stream_1 in the MPEG-2 system.
Pattern data on one, two or more horizontal scanning lines is described in one packet of the pattern data.
According to a second aspect of the present invention, there is provided a data recorder which comprises the data multiplexer mentioned above, and a recording means for recording, on a recording medium, the data multiplexed by the data multiplexer.
According to a third aspect of the present invention, there is provided a data multiplexing method which multiplexes at least digital motion picture data and pattern data. This method comprises the steps of: forming the digital moving picture data and the pattern data into packets of a predetermined format, each packet consisting of a header and an actual data region; adding, to the header of each packet, a flag to identify the moving picture data and the pattern data; and multiplexing the packets.
According to a fourth aspect of the present invention, there is provided a data recording medium where at least digital moving picture data and pattern data are multiplexed and recorded. In this recording medium, the digital moving picture data and the pattern data are formed into packets in a predetermined format, each packet consisting of a header and an actual data region; and a flag for identifying the moving picture data and the pattern data is added to the header of each packet; and the packets are multiplexed and recorded.
According to a fifth aspect of the present invention, there is provided a data demultiplexer for separating multiplexed data of at least packetized digital moving picture data and pattern data. This data demultiplexer comprises a detecting means for detecting a flag to identify the digital moving picture data and the pattern data from the packet thereof; a separating means for mutually separating the digital moving picture data and the pattern data in accordance with the flag detected by the detecting means; a moving picture data decoding means for decoding the moving picture data separated by the separating means; and a pattern data decoding means for decoding the pattern data separated by the separating means.
The data demultiplexer further comprises a time stamp detecting means for detecting a time stamp which indicates the timing to decode or display the digital moving picture data or the pattern data; and a control means for synchronously controlling the moving picture data decoding means and the pattern data decoding means in accordance with the time stamp detected by the time stamp detecting means.
The data demultiplexer further comprises an adding means for adding, as a signal of a different horizontal scanning line, the signal decoded by the pattern data decoding means to the signal decoded by the moving picture data decoding means.
And according to a sixth aspect of the present invention, there is provided a data demultiplexing method for separating multiplexed data of at least packetized digital moving picture data and pattern data. This data demultiplexing method comprises the steps of: detecting a flag to identify the digital moving picture data and the pattern data from the packet thereof, and also detecting a time stamp which indicates the timing to decode or display the digital moving picture data or the pattern data; mutually separating the digital moving picture data and the pattern data in accordance with the detected flag; and decoding the moving picture data and the pattern data thus separated.
In the data multiplexer and the data multiplexing method of the present invention, digital moving picture data and pattern data are formed into packets of a predetermined format, and a flag for identifying the moving picture data and the pattern data is added to the header of each packet. Therefore the pattern data inserted in a position on an arbitrary horizontal scanning line can be multiplexed with the moving picture data.
In the data recorder and the data recording medium of the present invention, the packetized moving picture data and pattern data of a predetermined format are recorded on the data recording medium with addition of a flag which identifies such data. Accordingly, the pattern data inserted on an arbitrary horizontal scanning line can be multiplexed and recorded with the moving picture data.
In the data demultiplexer and the data demultiplexing method of the present invention, the digital moving picture data and the pattern data are mutually separated in accordance with the detected flag. Therefore the digital moving picture data and the pattern data can be exactly decoded and displayed with certainty.
The above and other features and advantages of the present invention will become apparent from the following description which will be given with reference to the illustrative accompanying drawings.